Apparatus and method for monitoring a detection region of a working element

ABSTRACT

The invention relates to an apparatus and a method for monitoring a detection region ( 6 ) of a working element. The apparatus has at least one camera ( 5 ) for continuously detecting the detection region ( 6 ), and an evaluation unit, into which image information generated by the camera ( 5 ) is read. In the evaluation unit, a comparison of the image information to reference images, and/or a color-feature analysis, allow(s) the detection of endangered objects within at least one protection zone ( 7 ) in the detection region ( 6 ). If at least one endangered object is detected inside the protection zone ( 7 ), the evaluation unit disables the working element. In contrast, if no endangered object is located inside the protection zone ( 7 ), the evaluation unit enables the working element.

[0001] The invention relates to an apparatus and a method for monitoringa detection region of a working element.

[0002] The working element can be formed by, for example, a foldingpress that has at least one upper tool and one lower tool, whichcooperate to bend and bevel workpieces comprising pieces of sheet metal,in particular. For this purpose, the upper tool is guided toward thelower tool in a pressing movement, thereby deforming a piece of sheetmetal, which is disposed between the two tools, along a fold line.Folding presses of this type are potentially hazardous to the operator,because the workpiece must usually be guided manually during thepressing movement. Consequently, the operator's hands and fingers arenear the upper and lower tools, or near the squeezing and shearingpoints of the folding press or the workpiece, which puts him at risk forserious injury.

[0003] To make these detection regions safer, it is standard practice touse protective devices that disable the working element if the operatorhas inadvertently intruded into the region.

[0004] These protective devices can take the form of two-handed switchesthat protect the operator's hands by requiring the actuation of twolevers to initiate and maintain a potentially dangerous movement in afolding press. The operator must therefore keep both hands on thelevers, which safeguards him against injury during press operation.

[0005] A drawback of this device, however, is that other persons in thedetection region are unprotected. A further drawback is that theoperator cannot manually guide the workpiece during machining, which isperceived as problematic. The operator therefore often chooses todisable the protective device and guide the workpiece manually in thedetection region, without protection.

[0006] Safety light curtains are also used as protective devices. DE 3939 191 C3, for example, discloses such a device. In this case, thesafety light curtains comprise numerous pairs of transmitters andreceivers that respectively form a light barrier.

[0007] The light beams emitted by the transmitters and aimed at therespectively associated receiver cover a planar, two-dimensionalmonitoring region. It is possible to detect that a hand is approaching adetection region, whereupon the working element is disabled.

[0008] A safety light curtain of this nature is typically disposedvertically, and serves to bar access to a folding press. In themachining of larger pieces, it is advantageous to arrange the safetylight curtain horizontally to secure the region. A disadvantage of thisarrangement is that a plurality of safety light curtains is required forcompletely securing the detection region of this folding press,especially with respect to preventing access and securing the region.This requirement not only raises costs to an undesirable level, but isalso associated with complicated assembly, often with only insufficientspace available for the devices.

[0009] DE 196 19 688 A1 relates to a method for video monitoring ofoperator areas, such as of a press, in which a video camera opticallydetects the operator area to be monitored, and generates anelectronically-processable image of the open operator space, which thecamera supplies to an image processor, where it is stored.

[0010] Prior to each startup of the press, the video camera records animage of the operator area and compares the generated image to the imagestored in the image processor. The press can only be started up if thenew image is identical to the stored image.

[0011] A disadvantage of this method is that any deviation of a currentimage from the reference image disables the press, even if the deviationwould not pose a threat to the respective operator. This systempossesses a low availability, which unnecessarily limits the operatingtimes of the press.

[0012] It is the object of the invention to create a system that assuresreliable monitoring of a detection region of a working element withoutunnecessarily limiting its availability.

[0013] The object is accomplished by the features of claims 1 and 26.The dependent claims disclose advantageous embodiments and modificationsof the invention.

[0014] In accordance with the invention, for monitoring a detectionregion of a working element, at least one camera continuously detectsthe detection region.

[0015] The image information generated in the camera during thedetection is read into an evaluation unit.

[0016] This image information is used in a comparison to referenceimages that are stored in the evaluation unit, and/or in a color-featureanalysis, to detect endangered objects within at least one protectionzone in the detection region.

[0017] If at least one endangered object is detected within theprotection zone, the evaluation unit disables the working element,whereas the evaluation unit enables the working element if there is noendangered object in the protection zone.

[0018] A significant advantage of the protective device of the inventionis that a three-dimensional detection region of the working element canbe detected. One camera can perform multiple monitoring functions.Notably, a suitable selection of the monitoring region detected by acamera assures both access prevention and the securing of the region ofthe working element.

[0019] A further advantage is that endangered objects located within thedetection region detected by a camera, such as a person's hands orfingers, can be distinguished from non-endangered objects. Thecolor-feature analysis of the invention figures into this distinction.Also, the reference images can be selected such that they detect thenon-endangered objects located in a protection zone. Then a comparisonof the current image information to the reference images can be used toseparate and detect the endangered objects.

[0020] In principle, the image information can be compared to thereference images, or evaluated in a color-feature analysis, forassessing whether an endangered object is located in the protectionzone.

[0021] The two methods are advantageously evaluated in a combination.This can significantly increase the verification reliability of theapparatus according to the invention.

[0022] For example, the working element can only be enabled if the twomethods do not indicate the presence of an endangered object in theprotection zone. Therefore, the danger of non-detection of an endangeredobject can be greatly reduced.

[0023] The protective device according to the invention only disablesthe working element if an endangered object enters a protection zoneinside the detection region.

[0024] In the simplest case, the protection zone extends over the entiredetection region detected by the camera. The protection zone isadvantageously dimensioned as a defined partial section of the detectionregion through the input of parameters into the evaluation unit, orthrough a learning process. The protection zone can thus be preciselytailored to the danger points to be detected. This avoids monitoring ofareas that are not of concern in terms of safety, which considerablyincreases the availability of the protective device of the inventionwithout reducing the level of safety in the monitoring.

[0025] In an advantageous embodiment of the invention, the protectionzone can be allocated at least one warning zone, which preferablyadjoins the protection zone directly. If an endangered object enters thewarning zone, a warning signal is emitted, which provides an earlywarning for the operator or other person of the impending entry of anendangered object into the protection zone. The operator can thereforeundertake appropriate measures to prevent the endangered object fromentering the protection zone, thereby avoiding the disabling of theworking element. This prevents unnecessary downtime of the workingelement.

[0026] In an advantageous modification of the invention, numerousprotection zones and warning zones can be provided within a detectionregion, corresponding to the requirements of the respective application,in which instance the working element is only disabled if an endangeredobject is detected in at least one protection zone. Accordingly, awarning signal is emitted if an endangered object is detected in atleast one warning zone.

[0027] The invention is described below in conjunction with thedrawings. Shown are in:

[0028]FIG. 1: a front view of a working element formed by a foldingpress, with two cameras being disposed in front of the element formonitoring detection regions;

[0029]FIG. 2: a side view of the arrangement according to FIG. 1;

[0030]FIG. 3: a cross-section through a section of the arrangementaccording to FIG. 1, with a protection zone and a warning zone beingdisposed inside a detection region;

[0031]FIG. 4: a working element embodied as a printing press, having acamera for monitoring a monitoring region that extends over the regionof the feed and output mechanisms of the press;

[0032]FIG. 5: the printing press according to FIG. 4, having two camerasfor monitoring the region of the output mechanism and the feedmechanism;

[0033]FIG. 6: a region monitored by a camera, namely the paper feed atthe feed mechanism of the printing press according to FIG. 4 or 5; and

[0034]FIG. 7: a working element embodied as a welding robot, having acamera for monitoring a detection region in the region of access to thewelding robot.

[0035]FIGS. 1 through 3 illustrate an exemplary embodiment of a workingelement configured as a folding press 1, which is monitored with theapparatus of the invention for the purpose of avoiding putting anoperator at risk.

[0036] The folding press 1 serves to bend and shape workpieces 2,particularly pieces of sheet metal. An upper tool 3 and a lower tool 4,which cooperates with the upper tool, shape a workpiece 2. During apressing movement, the upper tool 3 and lower tool 4 are guided towardone another, so a workpiece 2 located between them is beveled or bentalong a fold line.

[0037] In the present embodiment, the folding press 1 has four adjacentpairs of upper tools 3 and lower tools 4. For machining the workpieces,an operator usually brings the workpieces 2 into predetermined positionsbetween the upper tool 3 and the lower tool 4. In the process, theoperator is particularly at risk of serious injury when he puts hishands or fingers into the region between the upper tool 3 and the lowertool 4. The movement of the workpiece 2 during the pressing process alsoposes a tremendous risk of injury for the operator.

[0038] The apparatus according to the invention, which constitutes acontactless protective device, is provided for protecting the operator.

[0039] The apparatus includes at least one camera 5, preferably a videocamera. This camera 5 detects a detection region 6 of the workingelement, corresponding to the aperture angle of the optics, not shown,of the camera 5. In the present embodiment, two cameras 5 are providedin front of the folding press 1; each camera 5 detects a detectionregion 6, in which two pairs of upper tools 3 and lower tools 4 arelocated.

[0040] As can be seen from FIGS. 1 through 3, the detection region 6monitored by a camera 5 forms a three-dimensional spatial area whosebase outline has a rectangular cross section. The long side of thedetection region 6 extends along the fold lines of the upper tools 3 andlower tools 4 located in the detection region 6. The cross-sectionalsurface of the detection region 6 tapers upward toward the camera 5,corresponding to the aperture angle of the optics of the camera 5.

[0041] The camera 5 is integrated into a housing that is seated in aform-fit on a mechanical holding device, not shown, such that theholding device is disposed at an incline above the upper tools 3 andlower tools 4. The mechanical holding device can be adjusted in allthree spatial directions for orienting the camera 5 relative to theupper tools 3 and lower tools 4. The adjustment is performedindependently of the camera 5, so the adjustment of the holding deviceis even maintained when the camera 5 is exchanged.

[0042] A separate illumination system, not shown, can be associated witheach camera 5 for achieving uniform illumination of the respectivedetection region 6.

[0043] An evaluation unit, also not shown, is provided in the housing ofthe camera 5 for evaluating the image information obtained by the camera5. The evaluation unit is formed by a microprocessor or the like.

[0044] In the evaluation unit, the image information is assessed so asto permit the detection of endangered objects. In particular, endangeredobjects and non-endangered objects are distinguished. Endangered objectsinclude the operator, more precisely his hands or fingers.Non-endangered objects include, for example, the front walls of thefolding press 1 or other static objects in the surrounding area of thefolding press 1, especially the workpieces 2 to be machined.

[0045] In accordance with the invention, in the evaluation unit, anassessment is performed to determine whether an endangered object islocated in a protection zone 7 inside the detection region 6. If this isthe case, the evaluation unit disables the working element to protectthe operator. If, in contrast, there is no endangered object in theprotection zone 7, the evaluation unit enables the operation of theworking element.

[0046] To this end, a binary switching signal is transmitted to thecontrol of the working element via a switching output connected to theevaluation unit.

[0047] In the evaluation unit, the evaluation is performed as follows:Depending on whether an endangered object is present in the protectionzone 7, the binary switching signal has a specific switching state. Therespective switching state is transmitted to the control of the workingelement, whereupon the element is enabled or disabled. The switchingoutput is advantageously connected to the control via a bus system.

[0048] To assure the necessary safety level in the respective monitoringprocess, the evaluation unit partially has redundant hardware. Thesoftware for the evaluation unit also has a safety standard thatcorresponds to the safety level. Finally, the bus system is alsoadvantageously embodied as a safety bus system.

[0049] In the simplest case, the protection zone 7 can be congruent withthe monitoring region detected by the camera 5.

[0050] The protection zone 7 is advantageously limited to the regionsinside the detection region 6, in which the operator is at risk. In thescenario illustrated in FIG. 3, the protection zone 7 represents athree-dimensional partial region of the detection region 6, with thelong-side border extending parallel to the fold lines of the upper tools3 and the lower tools 4 in the detection region 6, the tools beinglocated within the protection zone 7. Thus, the dangerous region at theupper tools 3 and lower tools 4 is detected directly with the protectionzone 7.

[0051] The embodiment illustrated in FIG. 3 has a warning zone 8 inaddition to the protection zone 7. The warning zone 8 is disposed infront of the upper tools 3 and lower tools 4, and directly adjoins theprotection zone 7. The protection zone 7 and the warning zone 8 haveapproximately the same dimensions, notably about the samecross-sectional surfaces.

[0052] A warning output, which controls a warning indicator, not shown,is associated with the warning zone 8 via the evaluation unit. In theevaluation unit, it is determined whether an endangered object islocated in the warning zone 8. Depending on the outcome, a binary signalis generated, with the respective switching state of the signal beingtransmitted via the warning output. If an endangered object isregistered in the warning zone 8, the warning indicator is activated bythe generated switching state, so the indicator emits an acousticaland/or optical warning signal.

[0053] This signals to the operator that an endangered object is locatedin the warning zone 8, and thus in the immediate vicinity of theprotection zone 7. In particular, the operator is informed that hisfingers or hands are in the vicinity of the protection zone 7, so theoperator can eliminate the threat of injury by removing his hands fromthe warning zone 8 without entering the protection zone 7, which wouldlead to an undesired disabling of the folding press 1.

[0054] In an advantageous modification of the invention, the directionof movement of an endangered object within the warning zone 8 isdetected. In this case, the warning indicator is only activated if anendangered object inside the warning zone 8 is approaching theprotection zone 7.

[0055] In principle, a detection region 6 detected by a camera 5 can bedivided into a plurality of protection zones 7 and warning zones 8.Here, a separate switching output is associated with a protection zone7, and a separate warning output is associated with each warning zone 8.

[0056] The evaluation unit disables the working element if at least oneendangered object is registered in at least one protection zone 7.

[0057] Depending on the application, a separate warning indicator can beprovided for each warning zone 8. As an alternative, a plurality ofwarning outputs can be associated with one warning indicator.

[0058] The switching states of the switching outputs and the warningoutputs can be visually indicated in a suitable way, which requiresappropriate display elements.

[0059] In the embodiment according to FIG. 3, the visual display can beeffected, for example, in the manner of a traffic light. If such a lightdisplays a red light, this means that an endangered object is located inthe protection zone 7. A yellow signal corresponds to the presence of anendangered object in the warning zone 8, with an empty protection zone7. A green signal indicates that there is no endangered object in eitherthe protection zone 7 or the warning zone 8.

[0060] The protection zone 7 and/or the warning zone 8 can bedimensioned, for example, through the input of parameters into theevaluation unit.

[0061] The evaluation unit can, for example, be connected to a computer,such as a PC, for starting up and configuring the protective device. Themouse of the PC can be used to graphically input the parameters for theprotection zone 7 and/or warning zones 8.

[0062] As an alternative, the protection zones 7 and/or warning zones 8can be dimensioned through a learning process prior to the startup ofthe protective device.

[0063] Furthermore, regions inside the detection region 6 that areextracted in the monitoring process can also be defined in the describedconfiguration options. These regions can overlap the protection zones 7.In the following operating phase of the protective device, these regionsare preferably activated at preset times. During these times, if anendangered object enters such a region, this does not lead to thedisabling of the working element or the emission of a warning signal.

[0064] The definition of these regions is especially practical if, forexample, dangerous tools of a working element are disabled at presetintervals, so the operator is not at risk in these regions during thesetime intervals.

[0065] The definition of the protection zones 7 and the warning zones 8during the configuration is application-specific, and is adapted to therespective shape of the workpieces 2 to be machined with the workingelement.

[0066] In the embodiment according to FIGS. 1 through 3, pieces of sheetmetal are bent. Their geometries can be read as CAD data files into theevaluation unit, so suitable protection zones 7 and/or warning zones 8can be defined accordingly.

[0067] The regions in which the operator is allowed to hold the bendingpart for machining are advantageously also read in with the CAD datafiles. The protection zones 7 and warning zones 8 can have acorrespondingly-adapted embodiment.

[0068] In a particularly advantageous feature, optical light beamsindicate the borders of the respective protection zones 7 to theoperator. For the beams, the apparatus of the invention includes atransmitter, which is actuated by the evaluation unit and emits lightbeams in the visible range. The optical light beams provide a visualindication of straight-line borders of the protection zones 7.

[0069] Finally, in the configuration of the protection device of theinvention, the device can learn about endangered objects andnon-endangered objects during a learning process.

[0070] In the apparatus of the invention, a camera 5 continuouslydetects a detection region 6, with the image information that has beengenerated in the camera 5 being read into the evaluation unit.

[0071] According to a first variation of the method of the invention, acolor-feature analysis serves in the evaluation of the imageinformation.

[0072] The image information of the camera 5 is then read, as colorvalues, into the evaluation unit. The color-feature analysis aids in thedistinction between endangered objects and non-endangered objects.

[0073] Each image of the camera 5 is formed by a pixel matrix, withspecific color values of the base colors of red, green and blue beingassociated with each pixel.

[0074] A threshold-value unit, which is a component of a neuronalnetwork, assesses these images. In principle, the color values of thedifferent base colors can be assessed with separate threshold valuesthat are generated in the threshold-value unit.

[0075] In the present embodiment, in the evaluation unit, a linearcombination of the individual color values of the base colors is formedfor each pixel of an image; the individual color values are weightedwith weighting factors that are stored in the evaluation unit or can bepredetermined by the unit. This linear combination is assessed with athreshold value that has been generated in the threshold-value unit. Inthis way, a binary image is created from the color image generated inthe camera 5. The threshold value and the weighting factors are adaptedsuch that the endangered objects are, for example, bright regions offoreground pixels that stand out against a dark background of backgroundpixels.

[0076] The threshold values and the weighting factors are advantageouslydetermined during the learning process. At this time, the colors of theendangered objects are learned. The endangered objects are preferablythe hands and/or fingers of the individual operating the workingelement.

[0077] In principle, the hands and/or fingers of numerous persons canalso be learned.

[0078] As an alternative for the case of endangered objects comprisingbody parts, it is required that the persons wear a protective coveringof a predetermined color. In this way, the parameters for the imageevaluations are adapted to the color of the protective covering.

[0079] In the binary images generated by the threshold-value unit, theendangered objects form connected regions of foreground pixels thatstand out against the background pixels. Non-endangered objects such asthe workpieces 2 and the working element form the background pixels.

[0080] At isolated points, the binary image can be noisy due to pixelerrors, so individual foreground pixels appear in the background region.These pixel errors can be eliminated through the application ofmorphological operators. In the process, isolated regions of foregroundpixels whose surface areas are smaller than a predetermined minimumsurface area are eliminated. These minimum surface areas are selected tobe significantly smaller than the surface area of the smallestendangered object to be detected.

[0081] In accordance with a second variation of the method of theinvention, the images that have been generated by the camera 5 and readinto the evaluation unit are compared to reference images stored in theevaluation unit for recognizing endangered objects within the protectionzones 7 and/or the warning zones 8.

[0082] In an advantageous embodiment of the invention, the images andreference images are converted into binary edge images prior to thecomparison. For this purpose, the amounts of the gradients of thebrightness distributions of an image or reference image are evaluated,preferably with a suitable threshold value. The binary edge imagesformed in this manner contain structures of lines on a homogeneousbackground, with the lines corresponding to the edges of the objectslocated in the detection region 6.

[0083] This evaluation renders the detection of objects extensivelyindependent of the respective illumination conditions, so fluctuationsin brightness, such as changing sunlight radiation, do not result inerroneous detections.

[0084] To further increase the verification reliability, the protectionzone 7 is advantageously bordered at least partly by a reference objecthaving a defined contrast pattern. The reference object can be formedby, for example, a disk that has a characteristic surface pattern, andis mounted to the folding press 1 beneath a lower tool 4 such that it ispositioned in the viewing field of the camera 5. The surface pattern ofthe disk can be embodied, for example, as a colored striped pattern, soit is clearly distinguished from the color patterns of the endangeredobjects.

[0085] The comparison of the current images to the reference imagecontaining the reference object allows the endangered objects in theprotection zone 7 to be detected with a high reliability.

[0086] This method does not include a feature analysis of the objectsentering the protection zone 7, so every such object is regarded as anendangered object.

[0087] In the machining of workpieces 2 by the working element, theworkpieces 2 can enter the protection zone 7 particularly atpredetermined times during which the disabling of the working element isundesirable.

[0088] For example, the operator must be able to insert and process aworkpiece 2 embodied as a bending part between the upper tool 3 andlower tool 4 of a folding press 1 without the folding press 1 beingunnecessarily shut down by the protective device.

[0089] In an advantageous embodiment of the invention, therefore, in alearning process prior to the startup of the folding press 1, the camera5 records the individual steps for machining a workpiece 2, therebyrecording and storing reference images for individual machining phases.The reference images specifically depict the workpiece 2 in differentmachining positions.

[0090] In the operating phase of the working element that follows thelearning phase, the camera 5 again records the same machining steps. Acomparison of the recorded images to the respective reference images canreveal the intrusion of endangered objects, such as a person's hands orfingers. The respective protection zones 7 and/or warning zones 8 can beselected to change over time for the individual machining steps.

[0091] A particular advantage of this is that the comparison to therespective reference images permits the distinction of endangeredobjects from the workpiece 2, which represents a non-endangered object.Consequently, the workpiece 2 located inside the protection zone 7 doesnot cause the protective device to unnecessarily disable the foldingpress 1. A suitable, time-dependent dimensioning of the protection zones7 and/or warning zones 8 allows the detection region to be flexiblyadapted to the changing marginal conditions.

[0092] This method can encompass the following steps, for example:

[0093] In the learning phase prior to startup, a machining process isperformed in its entirety with a workpiece 2 in the folding press 1.

[0094] First, the operator inserts the workpiece 2 into the foldingpress 1, so it lies inside the press 1. A retaining device may beutilized for this purpose. Because the upper tool 3 and the lower tool 4are deactivated in this phase, the protection zone 7 is dimensioned suchthat the operator can reach into the region between the upper tool 3 andthe lower tool 4. Particularly in this case, the protection zone 7 canalso be bridged and completely deactivated.

[0095] Afterward, the operator removes his hands from the workpiece 2and the fold line between the upper tool 3 and the lower tool 4, so apredetermined safety distance is exceeded. During this machining step,the protection zone 7 is dimensioned in the evaluation unit to encompassthe region of the upper tool 3 and the lower tool 4 up to this safetydistance.

[0096] A foot switch initiates the lowering of the upper tool 3 towardthe lower tool 4 until the workpiece 2 is held without play between theupper tool 3 and the lower tool 4. Thus, the operator can no longerinsert his hands or fingers between the upper tool 3 and the lower tool4, so the folding press 1 no longer poses a threat to him.

[0097] The operator can therefore safely orient the workpiece 2 manuallyon the folding press 1. As soon as the workpiece 2 is oriented correctlyon the folding press 1, it is recorded with the upper tool 3 and thelower tool 4 as a reference image, and stored in the evaluation unit.

[0098] The bending process, in which the workpiece 2 is bent upward, isthen initiated. The free end of the workpiece 2 is bent upward to anintermediate position. The bending process is only performed until asufficient spacing is present between the free end of the workpiece 2and the upper tool 3 to prevent the risk of injury to the operator dueto a so-called upper jaw clamp.

[0099] In this position, a second reference is recorded and stored; thisimage depicts the positions of the upper tool 3 and the workpiece 2.

[0100] During these processes, the operator is at no risk for injury, sothe protection zone 7 can be selected to be correspondingly small.

[0101] Finally, the bending process of the workpiece 2 is completed, atwhich point the operator must remove his hands from the region of theworkpiece 2, because the risk of injury is present again. A largerprotection zone 7, which is adapted to the safety distance that must bemaintained, is advantageously specified in this phase.

[0102] After the learning process has ended, the folding press 1 isenabled, with the workpiece 2 being machined in the same machiningsequence that was learned in the learning process.

[0103] The operator first inserts the workpiece 2 between the upper tool3 and the lower tool 4, which are deactivated at this time. Theprotection zone 7 is dimensioned such that this action does not lead tothe disabling of the folding press 1.

[0104] In the next machining step, the foot switch effects the loweringof the upper tool 3 until the workpiece is held without play between theupper tool 3 and the lower tool 4. In this phase, the protection zone 7is dimensioned such that an intrusion into the region of the fold lineresults in the disabling of the folding press 1.

[0105] The operator can then safely orient the workpiece 2 locatedbetween the upper tool 3 and the lower tool 4; the present embodiment ofthe protection zone 7 prevents the disabling of the folding press 1 dueto the manual access to the workpiece 2.

[0106] As soon as the workpiece 2 is oriented, the bending process isinitiated. The bending process is only started if the images currentlybeing recorded in the camera 5 match the reference image showing theoriented workpiece 2.

[0107] During the subsequent bending of the workpiece 2 to theintermediate position, the operator can manually guide the workpieceagain.

[0108] The current images of the camera 5 are compared to the secondreference image to ascertain whether the intermediate position has beenreached.

[0109] While the bending process continues from the intermediateposition, operator intrusion into the region of the workpiece 2 againleads to the shutdown of the folding press 1.

[0110] To check the function of the protective device of the invention,a self-test is performed at predetermined intervals. The self-test isadvantageously performed periodically and automatically, that is,without external activation.

[0111] In the present embodiment, both a static self-test and a dynamicself-test are performed.

[0112] The static self-test essentially checks whether predeterminedfixed points are present in the images generated by the camera 5. If thefixed points are absent, or have changed, an error message is generatedand the working element is disabled.

[0113] This static self-test utilizes the fact that the camera 5 remainsoriented precisely in terms of position on the holding device, socertain objects, such as parts of the working element or otherequipment, building walls or the like, remain unchanged in the detectionregion 6 detected by the camera 5. During a learning process prior tothe startup of the protective device, such objects are learned as fixedpoints and stored in the evaluation unit.

[0114] This static self-test is particularly used to check thefunctioning capability of the optical components of a camera 5.

[0115] In the dynamic self-test, a defined, preferably endangered, testobject is brought into the region of a protection zone 7 atpredetermined times. If this test object is not recognized at thepredetermined times, the working element is not enabled, or if it isoperating, it is disabled.

[0116] This dynamic self-test is advantageously performed before theprotective device is started up. In principle, the dynamic self-test canalso be performed during the operation of the protective device. In thiscase, however, it must be ensured that the location of entry of the testobject, or its embodiment, distinguishes it from the endangered objectsto be detected during the operation of the protective device. Afterward,the test object is verified independently of the detection of endangeredobjects, and therefore does not impair the verification reliability ofthe protective device.

[0117]FIGS. 4 and 5 illustrate embodiments in which a printing press 9constitutes the working element monitored by the protective device ofthe invention.

[0118]FIG. 4 shows a printing press 9 having a feeder 10 and an output.The feeder 10 forms the insertion region, in which paper sheets aredrawn from paper stacks 11 and fed into the printing apparatus of theprinting press 9. A chain conveyor 12 supplies the individual paperstacks 11, on pallets, to the feeder 10. In the region of the feeder 10,the paper stacks 11 are transported on a roller conveyor 13. After thepaper sheets have been printed, a second chain conveyor 14 in the outputregion transports them away from the printing press 9 in paper stacks 11stacked on pallets. In the regions of the chain conveyors 12, 14 and thefeeder 10, the traveling movements of the pallets with the paper stacks11 represent a risk of injury for the operator.

[0119] In known printing presses 9, these detection regions 6 aresecured by an enclosure that completely prevents operator access. Thisseverely and unnecessarily limits the visibility and accessibility ofthe printing press 9, however. In particular, it is impossible or verydifficult to position non-endangered objects in the detection region 6.

[0120] In the embodiment illustrated in FIG. 4, a camera 5 is mountedabove the printing press 9 such that the detection region 6 detected bythe camera encompasses the regions of the feeder 10 and the chainconveyors 12, 14.

[0121] Monitoring with the camera 5 is performed analogously to theembodiments of FIGS. 1 through 3. In particular, the detection region 6is again divided appropriately into protection zones 7 and possiblywarning zones 8, inside which endangered objects can be detected.

[0122]FIG. 5 shows a second embodiment of a protective device in aprinting press 9. The printing press 9 corresponds to the printing press9 according to FIG. 4. In contrast to the protective device according toFIG. 4, however, the protective device according to FIG. 5 has twocameras 5. The detection region 6 detected by the first camera 5encompasses the first chain conveyor 12 for supplying paper stacks 11 tothe printing press 9.

[0123] The detection region 6 detected by the second camera 5encompasses the second chain conveyor 14 for transporting paper stacks11 away from the printing press 9.

[0124] The detection regions 6 recorded by the cameras 5 are dimensionedsuch that their widths are larger than the widths of the chain conveyors12, 14. In this way, endangered objects can be detected before they haveentered the region of the chain conveyors 12, 14. For orienting theoperator, the borders of the protection zones 7 inside the detectionregions 6 can be marked with lines on the floor of the room housing theprinting press 9.

[0125] In the embodiments according to FIGS. 4 and 5, the paper stacks11 transported on pallets are learned as non-endangered objects andstored in the evaluation unit before the protective device is startedup.

[0126]FIG. 6 illustrates a feeder 10 of a printing press 9 that ismonitored by a protective device having a camera 5. The embodiment ofthe printing press 9 corresponds to that of the printing press 9according to FIGS. 4 and 5.

[0127] The feeder 10 essentially comprises a frame 15, inside which apaper stack 11 is disposed. A gripping element 16 draws paper sheetsfrom the top of the paper stack 11 into the printing apparatus, notshown, of the printing press 9.

[0128] The camera 5 is mounted above the feeder 10 such that thedetection region 6 detected by the camera 5 encompasses the top of thepaper stack 11 and the gripping element 16. The protection zone 7 insidethe detection region 6 is dimensioned to completely encompass theworking region of the gripping element 16, which executes movements thatcould injure the operator.

[0129]FIG. 7 shows an embodiment of a protective device that serves tomonitor the region in front of a working element embodied as a workingrobot. In the present embodiment, a welding robot 17 constitutes theworking robot.

[0130] The welding robot 17 is located in an enclosed production cell 18having an enclosure 19, which is provided with an access opening 20.Objects are introduced into and transported out of the production cell18 via the access opening 20. In addition, the operator has access tothe production cell 18 via the access opening 20. The region of theaccess opening 20 constitutes the detection region 6 detected by thecamera 5 of the protective device.

[0131] The detection region 6, which is again divided into one or moreprotection zones 7 and possibly warning zones 8, is located at adistance from the working region of the welding robot 17. Consequently,if an endangered object enters a protection zone 7, the welding robot 17is promptly disabled before the endangered object can pass through theprotection zone 7 to the welding robot 17. In this case, personsconstitute the endangered objects. Non-endangered objects, such as theworkpieces 2, that can enter a protection zone 7 are preferably learnedand stored in the evaluation unit prior to the startup of the protectivedevice.

[0132] The invention has been described in detail with respect topreferred embodiments, and it will now be apparent from the foregoing tothose skilled in the art, that changes and modifications may be madewithout departing from the invention in its broader aspects, and theinvention, therefore, as defined in the appended claims, is intended tocover all such changes and modifications that fall within the truespirit of the invention.

LIST OF REFERENCE CHARACTERS

[0133] (1) Folding press

[0134] (2) Workpiece

[0135] (3) Upper tool

[0136] (4) Lower tool

[0137] (5) Camera

[0138] (6) Detection region

[0139] (7) Protection zone

[0140] (8) Warning zone

[0141] (9) Printing press

[0142] (10) Feeder

[0143] (11) Paper stack

[0144] (12) Chain conveyor

[0145] (13) Roller conveyor

[0146] (14) Chain conveyor

[0147] (15) Frame

[0148] (16) Gripping element

[0149] (17) Welding robot

[0150] (18) Production cell

[0151] (19) Enclosure

[0152] (20) Access opening

1. An apparatus for monitoring a detection region (6) of a workingelement, having at least one camera (5) for continuously detecting thedetection region (6), further having an evaluation unit, into whichimage information that has been generated by the camera (5) is read, theinformation being used in a comparison to reference images stored in theevaluation unit, and/or in a color-feature analysis, to detectendangered objects within at least one protection zone (7) inside thedetection region (6), wherein, when at least one endangered object isdetected within the protection zone (7), the working element isdisabled, and the evaluation unit enables the working element if noendangered object is located inside the protection zone (7).
 2. Theapparatus according to claim 1 , characterized in that a switchingoutput that is guided from the evaluation unit to the working elementassumes a defined switching state, depending on whether an endangeredobject is located in the protection zone (7), and the working element isenabled or disabled, depending on this switching state.
 3. The apparatusaccording to claim 1 or 2 , characterized in that, in addition to theprotection zone (7), at least one warning zone (8) is defined inside themonitoring region detected by the camera (5), with the evaluation unitactivating a warning indicator if an endangered object is located in thewarning zone (8).
 4. The apparatus according to claim 3 , characterizedin that the warning indicator is connected to the evaluation unit by wayof a warning output, with the warning indicator being activated ordeactivated, depending on the switching state of the warning output. 5.The apparatus according to claim 3 or 4 , characterized in that thewarning indicator emits an optical and/or an acoustical warning signal.6. The apparatus according to one of claims 3 through 5, characterizedin that the warning zone (8) borders the protection zone (7).
 7. Theapparatus according to claim 6 , characterized in that the direction ofmovement of an endangered object located inside the warning zone (8) canbe detected.
 8. The apparatus according to claim 7 , characterized inthat the warning indicator is only activated if an endangered objectlocated inside the warning zone (8) is moving toward the protection zone(7).
 9. The apparatus according to one of claims 3 through 8,characterized in that a plurality of protection zones (7) and warningzones (8) is provided, with a switching output being associated witheach protection zone (7) and a warning output being associated with eachwarning zone (8).
 10. The apparatus according to claim 9 , characterizedin that the evaluation unit disables the working element if anendangered object is located in at least one protection zone (7). 11.The apparatus according to one of claims 3 through 10, characterized inthat the dimensions of the protection zones (7) and warning zones (8)can be selected through the input of parameter values into theevaluation unit.
 12. The apparatus according to one of claims 3 through11, characterized in that the dimensions of the protection zones (7) andwarning zones (8) can be predetermined through a learning process. 13.The apparatus according to one of claims 3 through 12, characterized inthat display elements visually indicate the switching states of theswitching outputs and warning outputs.
 14. The apparatus according toone of claims 1 through 14 [sic], characterized in that regions insidethe detection region (6) can be extracted for predetermined timeintervals, so if endangered objects enter these regions, the workingelement is not disabled via a switching output, and the warningindicator is not activated via a warning output.
 15. The apparatusaccording to one of claims 1 through 13, characterized in that theborder of a protection zone (7), which extends, at least by sections, ina straight line, can be visually represented by a visible light beam.16. The apparatus according to one of claims 1 through 15, characterizedin that the evaluation unit, with the camera (5) or cameras (5), isconnected via a safety bus system to the control of the working element.17. The apparatus according to one of claims 1 through 16, characterizedin that the camera (5) is seated in a form-fit on a mechanical holdingdevice, which can be adjusted in the three spatial directions,independently of the camera (5).
 18. The apparatus according to one ofclaims 1 through 17, characterized in that an active, separateillumination system is associated with the camera (5), or each camera(5).
 19. The apparatus according to one of claims 1 through 18,characterized in that the working element is formed by a folding press(1), which has at least one upper tool (3) that cooperates with at leastone lower tool (4).
 20. The apparatus according to claim 19 ,characterized in that the protection zone (7) encompasses the fold linebetween the upper tool (3) and the lower tool (4).
 21. The apparatusaccording to claim 19 or 21 , characterized in that the folding press(1) includes numerous pairs of cooperating upper tools (3) and lowertools (4), with a camera (5) monitoring a predetermined number of suchpairs of upper tools (3) and lower tools (4).
 22. The apparatusaccording to one of claims 1 through 18, characterized in that theworking element is formed by a printing press (9) having a feeder and anoutput.
 23. The apparatus according to claim 22 , characterized in thatat least one camera (5) detects the feeder (10) and/or the output of theprinting press (9) as a detection region (6).
 24. The apparatusaccording to claim 22 , characterized in that the paper-intake region atthe feeder (10) of the printing press (9) can be detected as a detectionregion (6) by a camera (5).
 25. The apparatus according to one of claims1 through 24, characterized in that a working robot constitutes theworking element.
 26. The apparatus according to one of claims 1 through25, characterized in that persons constitute the endangered objects. 27.The apparatus according to one of claims 1 through 26, characterized inthat human hands and/or fingers constitute the endangered objects.
 28. Amethod for monitoring a detection region (6) of a working element bymeans of an apparatus according to one of claims 1 through 27, themethod comprising the following steps: at least one camera (5)continuously detects a detection region (6); the image informationgenerated in the camera (5) during the detection is read, in the form ofcolor values, into an evaluation unit; the read-in color values are usedto distinguish endangered objects from non-endangered objects; and if atleast one endangered object is detected within at least one protectionzone (7) in the detection region (6), the evaluation disables theworking element, whereas the evaluation unit enables the working elementif no endangered object is located in the protection zone (7).
 29. Themethod according to claim 28 , characterized in that an image generatedby the camera (5) is read into the evaluation unit in the form of apixel matrix with different color values; and in the evaluation unit,for distinguishing endangered objects from no-endangered objects, thecolor values are assessed with a threshold-value unit, with binaryimages being created from the read-in images.
 30. The method accordingto claim 29 , characterized in that the threshold-value unit is acomponent of a neuronal network.
 31. The method according to claim 29 or30 , characterized in that three color values of the base colors of red,green and blue are associated with each pixel of an image that has beenread into the evaluation unit, and a linear combination is created fromthe individual color values that have been weighted with predeterminableweighting factors in the evaluation unit; and the linear combination ofcolor values is assessed with the threshold-value unit.
 32. The methodaccording to claim 31 , characterized in that, for determining thethreshold value or values of the threshold-value unit, and/or theweighting factors, the colors of the endangered objects are learned in alearning process.
 33. The method according to one of claims 29 through31, characterized in that, if endangered objects comprising persons,their hands and/or their fingers are present, the objects have aprotective covering of a predetermined color, with the threshold valueor values of the threshold-value unit being adapted to the color of theprotective covering.
 34. The method according to one of claims 29through 33, characterized in that, in a binary image generated by thethreshold-value unit, the endangered objects form a connected region offoreground pixels; and individual foreground pixels in the backgroundsurrounding this region are eliminated from regions with backgroundpixels by means of morphological operators.
 35. A method for monitoringa detection region (6) of a working element by means of an apparatusaccording to one of claims 1 through 27, the method comprising thefollowing steps: at least one camera (5) continuously detects adetection region (6); the image information generated in the camera (5)during the detection is read into an evaluation unit; endangered objectsare detected inside at least one protection zone (7) in the detectionregion (6) through a comparison of the image information to referenceimages stored in the evaluation unit; and if at least one endangeredobject is detected within the protection zone (7), the evaluationdisables the working element, whereas the evaluation unit enables theworking element if no endangered object is located in the protectionzone (7).
 36. The method according to claim 35 , characterized in that,for assessing the images and reference images, the images are convertedinto binary edge images through the assessment of the amounts of thegradients of their brightness distributions.
 37. The method according toclaim 35 or 36 , characterized in that the protection zone (7) isbordered by a reference object having a defined contrast pattern thatforms at least a portion of the reference image or a reference image.38. The method according to one of claims 35 through 37, characterizedin that, during a learning process, the machining steps for a workpiece(2) that constitutes a non-endangered object are detected with theworking element by the camera (5); and, for distinguishing endangeredobjects from non-endangered objects, the recorded images are compared tothe reference images recorded during the learning process.
 39. Themethod according to claim 38 , characterized in that the protectionzones (7) and/or the warning zones (8) can be changed over the course ofthe machining steps.
 40. The method according to one of claims 28through 39, characterized in that a self-test is performed atpredetermined intervals for checking the device function.
 41. The methodaccording to claim 40 , characterized in that a static self-test isperformed, in which the presence of predetermined fixed points in theimages generated by a camera (5) or the camera (5) is checked.
 42. Themethod according to claim 40 or 41 , characterized in that a dynamicself-test, in which the presence of a test object brought into theprotection zone (7) is checked, is performed at predetermined times.